Improved optimisation of radiation dose delivery to tumours with improved sparing of normal tissues is an ongoing goal of radiotherapy practice. Advanced radiotherapy techniques are constantly improving to achieve this goal. However, these techniques are more complex to deliver. Hence verifying the source of dose errors is increasingly challenging. Accurate verification of treatment delivery for advanced radiotherapy becomes increasingly important in mitigating dose delivery errors which may compromise clinical outcome. This dissertation investigated treatment dosimetry verification for two different radiotherapy delivery systems i) Open gantry linear accelerator and ii) Helical TomoTherapy HI-ART ® (HT).
Part (i) Open gantry linear accelerator - novel prototype hybrid EPID based dosimeters were developed for treatment verification to combine geometric and dosimetric verification in a single system. Initial work on dose response for standard EPIDs provided a more consistent understanding of EPID under-dose response for small monitor units (MUs).
The dose response linearity of a standard a-Si EPID was evaluated for different combinations of linac, image acquisition settings and imaging data processing methods. EPID nonlinear response was demonstrated to be primarily due to gain ghosting affects in the a-Si photodiodes. This work has resolved some of the inconsistencies in the literature regarding EPID dose response and proposes a simple yet robust pixel-to-dose calibration method for EPID-based IMRT dosimetry..
